The prior art is familiar with certain techniques that determine the dimensions of an object without physical contact to the object. For example, U.S. Pat. No. 6,064,759 shows a method for measuring structural detail of an object. A laser is arranged at an angle to the surface of the object and a recording device is employed at normal incidence to the surface. An image of the object is analyzed using known methods of image processing.
Three-dimensional measurement methods include an illumination technique disclosed in U.S. Pat. Nos. 4,645,348 and 4,846,577. In this technique, a “pattern projector” projects light through a mask, creating a light pattern on a surface of an object. A sensor, normally a CCD or CMOS camera, detects the pattern on the object, and the object contour is reconstructed using known triangulation methods. However, this technique results in a significant perspective distortion, rendering a projected light pattern that is not sharp.
At the “International Conference on Computer Simulation,” held in January 1998 in Bombay, India, Jean-Yves Bouguet and Pietro Perona disclosed a method of three-dimensional detection of objects based on “moved structural light”. This method projects an image of a rod-shaped shutter by introducing an oblong shutter body into the beam of a light source. In connection with this method, the illumination method disclosed in U.S. Pat. No. 6,529,627 is used for three-dimensional modeling of an object by using a light source that is inclined at an angle to the object, or shifted to a region of interest of the object, instead of using the shutter body. According to the method of Bouguet and Peron and U.S. Pat. No. 6,529,627, in addition to illuminating the object, movement of the shutter body or the illumination source is at a right angle to the illumination direction, so that the surface of the object is swept by the illuminating rays once per time period. Parallax effects are detected with two walls in the background of the object, which are arranged at a right angle with respect to each other. The parallax effects are taken into consideration during a correction when triangulation is performed. However, a corresponding correction with the help of background walls is required; thus the movement necessitates complex synchronization. Moreover, the method of Bouguet and Perona does not result in detailed measurements because the shutters do not provide good contrast; this procedure is also not effective when applied to dark objects.
A perspective view of a device previously designed by the patent applicant hereof, to measure the dimensions of an object, is shown in FIG. 1. The device of FIG. 1 is based on projection of light from a laser 91 in a plane E4 intersecting a surface 95 of an object 94. Plane E4 is at a right angle with respect to an axis 93 along which object 94 is moved longitudinally relative to the laser (or vice versa). In FIG. 1, object 94 is a part of an “endless profile,” that is, an object being manufactured in strip or sheet form. A laser line 96 forms at the intersection of laser plane E4 with surface 95. A CCD camera 92, arranged at an angle to axis 93, obtains an image of laser line 96 so that a contour of object 94 can be calculated based on distortion of laser line 96, using image processing such as triangulation.
A device similar to that shown in FIG. 1, including a laser and a CCD camera, can perform a panoramic measurement of an object. For example, the device can measure in several directions orthogonal to an axis in which the device advances relative to the object. However, factory alignment and calibration of laser(s) is time-consuming and thus expensive; safety regulations also apply to many laser based devices, further increasing their cost.